Is VSMUL.VV the same as VMUL followed by a shift?
No. VSMUL defines fixed-point rounding and saturation behavior, including vxsat on saturation.
VSMUL.VV
RISC-V VSMUL.VV Instruction Details
Instruction ManualR-typeSigned fixed-point fractional multiply with vxrm rounding and saturation.
Instruction Syntax
vsmul.vv vd, vs2, vs1, vm
Operand Breakdown
Destination rd: register receiving the operation result.
Source rs1: register holding the first operand.
Source rs2: register holding the second operand.
VVector Operations
Instruction Behavior
VSMUL.VV computes signed SEW-width products, scales by SEW-1 bits with vxrm rounding, then saturates to an SEW-width result; saturation sets vxsat.
Quick Understanding & Search Notes
VSMUL.VV is for fixed-point fractional multiplication, not ordinary integer multiply-low truncation.
The product is scaled by SEW-1 bits and rounded according to vxrm.
Out-of-range results saturate and set vxsat.
Use VMUL/VMULH forms for ordinary integer multiplication.
Common Usage Scenarios
Fixed-point DSP
Understand this scenario with real code like «vsmul.vv v8, v12, v4, v0.t».
Audio/video processing
Understand this scenario with real code like «vsmul.vv v8, v12, v4, v0.t».
Overflow-safe computation
Understand this scenario with real code like «vsmul.vv v8, v12, v4, v0.t».
Pre-Use Checklist
Syntax Check
- Confirm the current instruction format is R-type.
- Confirm the operand order matches the example.
Semantic Check
- Ensure the destination register usage is compatible with the calling convention.
- Confirm this is not the lower-level form of a pseudo-instruction expansion.
Pitfalls / Common Confusions
This is a fractional multiply: the product is shifted right by SEW-1, not simply truncated.
Rounding follows vxrm; saturation sets vxsat.